The present invention concerns the application of infrared thermometry to the measurement of the temperature of wires, bars or tubes and metal sheets movable in the direction of their length (hereafter the word "wire" will be used to designate also bars and tubes).
It also applies to the control of this temperature using such a measurement.
French Pat. No. 2 109 406 filed on Oct. 15, 1970 by the Laboratoires d'Electronique et de Physique Appliquee (LEP) and the grant of which was published on May 26, 1972, describes a process and a device for measuring the temperature of wires, called long-limbed cylindrical bodies in the patent, moving in the direction of their length, in which the wire whose temperature it is desired to measure is caused to pass in front of a black background at a uniform temperature and a parallel beam emitted by the assembly of the black background and said wire is focused on the sensitive element of an infrared detector, the output signal of the detector being representative of the temperature of said wire and substantially independent of the movement of the wire in relation to the black background. The focusing is achieved by means of a flat swinging mirror and a lens transparent to the infrared.
Though the use of a parallel beam scanning the wire and the black background by means of the swinging mirror has the advantage of providing a measurement of the temperature independent of the position of the wire in relation to the black background, the device of French Pat. No. 2 109 406 has the disadvantage of limiting considerably the optical efficiency of the system since a very small proportion of the infrared rays, namely those which are substantially parallel to the optical axis of the system, are focused on the sensitive element of the detector and are then converted into a usable electrical signal, this signal being cancelled out moreover preferably when the temperature of the wire is identical to that of the black background by using a differential measurement between the emission of the black background alone and of the black background on which a fraction of the wire is superimposed.
The present invention aims at improving the process and the device of the above-mentioned patent by using a much larger fraction of the infrared rays coming from the wire and the black background. For this, instead of focusing by means of a lens solely the infrared rays substantially parallel to the optical axis reflected by at least one flat mirror, a much greater part of the infrared radiation emitted by the black background and the wire or an edge of the metal sheet, the temperature of which it is desired to measure, is collected for example by means of at least one concave spherical mirror.
The invention provides then a process for measuring, by infrared thermometry, the temperature of a wire or a metal sheet moving in the direction of its length in front of a black background at a constant temperature, according to which substantially the whole of the infrared radiation emitted by a portion of said wire, or said metal sheet, at a given solid angle is collected and applied to the sensitive element of an infrared detector during certain periods of time.
The invention also provides a device for implementing this process, this device comprising at least one flat swinging mirror, which reflects in a certain direction all the infrared radiation emitted by a portion of said wire or metal sheet and the black background within a given solid angle, and at least one concave spherical mirror which collects the infrared beam reflected by said flat swinging mirror and directs this beam thus collected on to said sensitive element.
It might be thought a priori that the fact of not being limited to the infrared rays substantially parallel to the optical axis emitted by the portion examined of the wire or metal sheet and the surrounding black background would increase the influence on the measurement of the movements of the wire or metal sheet. Now, it has been established however--and figures will be given in this connection in the detailed description which follows--that this influence is reduced if it is arranged for the wire or metal sheet to oscillate about a position of equilibrium and if means are provided for integrating the signal emitted by the infrared radiation detector so as to have a statistical response in which the fluctuations due to the movement of the wire or metal sheet are counterbalanced.